1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an apparatus for driving a light source that increases the variable range of luminance and decreases power consumption.
2. Discussion of the Related Art
A liquid crystal display (LCD) device displays images using the electrical and optical properties of liquid crystal. A typical LCD device includes an LCD panel that displays images using a pixel matrix, and a driving circuit that drives the LCD panel. As LCD panels do not emit light, a backlight unit is provided to transmit light into the LCD panel to produce a viewable image. The LCD panel controls the transmittance of light emitted by the backlight unit by changing the alignment of liquid crystal according to a data signal applied to each sub pixel of the pixel matrix to thereby display images.
Backlight units may be broadly classified as either edge type or direct type units. In case of the edge type backlight unit, a light source is provided at a lateral side of a light-guiding plate and light emitted from lamps is supplied to the LCD panel through a light-guiding plate and a plurality of diffusion sheets. The direct type backlight unit is typically used with large-sized LCD panels and includes a plurality of light sources arranged at regular intervals at a lower surface of LCD panel to supply light to the entire lower surface of LCD panel.
The light source of the backlight unit may include a cylindrically shaped lamp such as a Cold Cathode Fluorescent Lamp (CCFL) or an External Electrode Fluorescent Lamp (EEFL). An EEFL lamp has electrodes formed externally to a cylindrical tube. The lamp of the backlight unit is driven by an inverter that supplies a tube current by changing a DC driving voltage to an AC driving voltage and stepping up the level of the AC driving voltage.
When used with large sized LCD devices, an edge type backlight unit typically uses a plurality of lamps. However, since the plurality of lamps provided in the related art LCD devices are driven by a single inverter, the variable range of luminance emitted from the lamps is limited, and power consumption is relatively high even in applications that display text and that do not need the higher luminance used for displaying moving images.